Sheeting knife construction for bread wrapping machines



Oct. 19, 1965 F. w. GREENOUGH 3, ,38

SHEETING KNIFE CONSTRUCTION FOR BREAD WRAPPINIG MACHINES Filed June 12, 1963 FIG. 2 WEB 23 TRAVEL 32 QIG INVENTOR 33 2 {0 IIMH M ATTORNEY United States Patent 3,212,383 SHEETING KNIFE CONSTRUCTION FOR BREAD WRAPFING MACHINES Francis W. Greenough, Spartanburg, S.C., assignor to W. R. Grace 8; Co., Duncan, S.C., a corporation of Qonnecticut Filed dune 12, 1963, Ser. No. 287,374 4 Ciaims. (til. 83-564) This invention relates to improvements in bread wrapping machines wherein the bread is enfolded in a continuous web of clear, flexible sheet material which may or may not have an underlying continuous narrower band of printed waxed paper. In particular the invention relates to a special knife construction for severing these webs into sheets as they are wrapped about the girth of the bread loaf, to the severing method and to the sheets produced.

Bread wrapping machines of the type to which this invention applies are known in the art. Exemplary disclosures of such machines are found in HoppeU.S. Patent 2,878,629 (March 24, 1959) and Tokos et al. US. Patent 3,064,403 (November 20, 1962). The entire disclosure of each of these patents is incorporated herein by reference. In all known machines of this type the knife used to sever the partially Wrapped web has a sawtooth blade. An identical or essentially similar blade is shown in Bell et al.-U.S. Patent 2,724,426 (November 22, 1955) especially in FIGURE 9 of the drawings thereof. Although this latter patent does not relate to the wrapping mechanism as such, its entire disclosure is also incorporated by reference with particular emphasis upon that portion relating to the sawtooth cutting blade and the cuts made thereby as illustrated in FIGURE 17 of the patent.

The sawtooth cutting blade on knives used in these prior machines was necessary for obtaining good cuts through the wax coated wrapper web or through the wax coated band used in conjunction with clear, flexible wrapping film. The wrapper sheets produced in machines using such knives consequently have cut edges which match the sawtooth configuration of the knife blade over their entire width.

Such sheets were satisfactory for producing strong bread packages from previously known wrapping materials including waxed paper; or transparent films such as cellophane, non-oriented polyethylene and the like with narrower underlying pre-printed waxed paper bands.

Recently there has been greatly increased interest in and demand for oriented thermoplastic, e.g., uniaxially oriented and/or biaxially oriented polypropylene films as a wrapping material for bread. Biaxially oriented polypropylene is of particular interest, primarily due to the extremely high clarity, good physical strength and very low water vapor permeability that such film possesses. However, one particularly vexatious problem has deterred complete acceptance of oriented films in bread wrapping applicaton. Since these films are characterized by easy tear propagation, the usual sawtooth cut edges in wrapper sheets made therefrom present a plurality of potential tear initiation points, and weaker bread packages often result. Thus, the frequent handling operations of the wrapped loaves in transit from the bakery to the ultimate consumer can cause tears around the girth of the loaf at any of the potential tear points and consequent separation of the package into two portions. In addition, when the loaf is opened by the consumer, the end label often adheres sufficiently to the end fold to initiate a tear which may propagate in virtually any direction.

It is a principal object of this invention to provide sheeting knife constructions which obviate these problems.

3,Zl2,383 Patented Oct. 19, 1965 Another object of this invention is to provide a method of cutting webs of oriented thermoplastic films in a manner which produces sheets having no potential tear propagation points. A specific object of the invention is to provide a knife construction and method for cutting webs of oriented thermoplastic films having an underlying narrower waxed paper band so as to produce sheets having a minimum number of potential tear propagation points. Yet another object is to provide an improved bread wrapping material comprising specially cut sheets of oriented thermoplastic film having an underlying narrower band of waxed paper. Further objects and advantages of the invention will become apparent after condsidering the following more detailed disclosure together with the accompanying drawings, in which:

FIGURE 1 is a front elevational view of a knife construction of this invention with the straight edge portion terminating at the gullet of the teeth of the sawtooth portion.

FIGURE 2 is a sectional view taken substantially on line 22 of FIGURE 1;

FIGURE 3 is a sectional view taken substantially on line 33 of FIGURE 1;

FIGURE 4 is a schematic illustration of the operation of the knife, and

FIGURE 5 is a plan view of a sheet of bread Wrapping material produced by the knife of FIGURE 1;

FIGURE 6 is a front elevational view of a knife construction of this invention with the straight edge portion terminating at the apex of the teeth of the sawtooth portion.

The detailed description places particular emphasis upon the knife designed to cut webs of thermoplastic film having an underlying band of waxed paper. This knife is shown in FIGURES 1-3. It has been assumed for the purposes of illustrating the invention that the underlying narrow waxed paper band is located at about the center of the film web, as is the usual practice.

The knife shown in FIGURES "1-3 comprises three separate and distinct blade portions 11, 12, and 13. Each of the portions 11 and 13 is designed to make an essentially straight edge cut. These portions comprise a blade body 14 the lower end of which is preferably beveled off at an angle a to result in a relatively sharp cutting edge 16. For universal applicability, the bevel angle a can suitably be about 25 or less, but preferably is between about 5 :and about 15 to provide a very sharp cutting edge. If polyolefin (e.g., polypropylene) films only are to be used, the sharpness of the cutting edge 16 is not critical, and these edges may in fact be quite blunt. This is explained by the fact that the polyolefin films can be severed by melting, so that good cuts are obtained simply by heating the blade portions 11, 13 to a suitable temperature.

In all cases, the cutting edge of each of the straight blade portions tapers downwardly away from the sawtooth portion at a angle b. The taper angle b must be at least 2". Taper angles of 2 or more are required so that at least a part of each straight blade cutting edge is below the plane of the apices of the teeth in the sawtooth portion so as to provide the necessary sequence of cutting actions that is more fully described hereinbelow. The upper limit to the taper angle b is in the vast majority of cases restricted solely by space limitations in the cutting section of presently know bread wrapping machines into which the improved knife construction is to be incorporated. It has been established that in any case the angle is not required to be any greater than 2. The sawtooth portion of the knife construction comprises a body 19 from which a plurality of teeth 20, terminating in apices 18, project. The pitch of the teeth, or in other Q) words the number of teeth per linear inch, is not critical. In actual practice the sawtooth portion used has been made to have a pitch of about .375 which is substantially the same as the pitch of blades previously used. As best seen in FIGURE 3, the sides 17 of the teeth in the sawtooth portion are also beveled in the same direction and at about the same angle as the straight blade portions.

It is not necessary, but almost always preferred for the purposes of this invention that the individual blade portion be so designed that the cutting edge 22 of the sawtooth portion and the cutting edge 16 of the straight blade portions meet at the base 22 of a tooth gullet at each end of the sawtooth portion, as illustrated in FIG. 1 of the drawings. The cutting edge 16 of the straight blade portions may also meet at the apex 18 of the tooth at each end of the sawtooth portion as illustrated in FIG- URE 6.

The knife of this invention may be fabricated from a single unitary blank, or more preferably (as shown) the three blade portions may be separately manufactured and then assembled on a unitary blade holder 23. Each of the three portions can be made up of two or more separate segments, e.g., segments 12a,12b, if desired for any particular reason. Assembly can be accomplished in any suitable manner. In the illustrated preferred embodiment matching holes are drilled through the blade portions and the blade holder, the various blades are inserted in the slot 24 in the holder and retained in place by flathead cap screws 25 or the like.

In most cases, in order to aid in obtaining optimum essentially straight side cuts, it is desirable to heat the straight blade portions of the knife. This can be done in a variety of ways. In the illustrated preferred embodiment heating is obtained by inserting commercially available electrically powered cartridge heaters into bores 26 provided therefore in at least those portions of the blade holder which mount the straight blade portions. Al-

simultaneously at the juncture of the straight blade portions with each end of the sawtooth portion. In those assemblies where the straight blade portions meet the sawtooth portion at the apex of a tooth, the cutting edges of the former portions are essentially completely below the plane of the tooth apices and the straight cuts are essentially completed before there is any cutting action by the sawtooth blade. In effect then, the two types of cuts are made seriatim, rather than as described immediately hereinabove.

In all cases, it is necessary in practicing the method of this invention to cut at least partially in from each side of the film web toward the center before attempting to begin the sawtooth cut. Attempts to cut the entire width though it is not necessary to do so, the sawtooth blade portion may also be heated if desired.

The amount of desired heating will vary with the type of biaxially oriented film in the wrapping material. For oriented polypropylene films the heat supplied should be sufiicient to maintain the temperature at the cutting edge of the straight blade portions in the range of from about 425 to about 500 Fahrenheit, preferably about 450 Fahrenheit. Temperatures suitable for other films will be readily ascertainable by those skilled in the art. The sawtooth portion is usually heated to temperatures of about 200-250 Fahrenheit, althought, as abovenoted, heating of this portion is not required.

The improved knife of this invention is particularly adapted for, though not restricted to, use in the environment of wrapping machines of the type disclosed in the aforementioned Hoppe and Tokos et al. patents. FIG- URE 4 schematically illustrates the operation of the improved knife in the machine shown in FIGURE 1 of the Hoppe patent. In FIGURE 4 it is seen that the knife (generally designated 10) operates in conjunction with a shear bar 29. The underlying band of printed wax paper 39 travels over this shear bar, and the film web 31 is interposed between the band and the knife. Travel of the web and band is momentarily halted. The knife rotates across the wrapping material and in cooperation with the shear bar servers the web and band. The knife is withdrawn. After another suitable length of wrapping material is wrapped around the bread loaf and drawn over the shear bar the knife is again actuated.

Because of the design of the improved knife, the cutting action first proceeds simultaneously from each side edge of the web on an essentially straight line. After at least about 25% of each side of the film web is cut, cutting action of the sawtooth portion in the illustrated knife begins to proceed together with continued cutting by the straight blade portions. Finally the web is fully severed when the respective cutting actions are completed substantially of the film web at the same time or to make the sawtooth cut first invariably result in jagged and/or irregular edges in the straight cut portions, or, at best, straight cut portions not at a right angle to the side edge of the web.

FIGURE 5 illustrates a sheet 51 of wrapping material prepared in accordance with the teachings of this invention. The leading edge 32 of the sheet has essentially straight right angle cuts over substantially the entire width of the film-only areas and a serrated cut extending substantially across the width of the film-paper band area. The serrated cut width may be slightly less than, equal to, or slightly greater than the width of the underlying paper band. In the leading edge of the sheet the teeth of the serrate cut extend outwardly from the staright edge. The

serrate cut and each of the straight cuts meet at the base of a gullet of such teeth. The trailing edge 33 of the sheet has a cut which matches the leading edge cut. In the trailing edge the points of the teeth in the serrate portion of the cut lie substantially on the line of the straight cut portions, and the distinct cut portions meet at the apex of such teeth. The edge 34 of the web from which sheet 51 has been served constitutes the leading edge of the next succeeding sheet 52.

In wrapping a loaf of bread for example, the sheet is drawn about the girth of the loaf and the cut edges overlapped and heat sealed together. In practice either cut edge may outlap the other. It will usually be preferred to use the trailing edge 33 of the sheet illustrated in FIGURE 5 as the outside or exposed layer in the overlapped area because this edge has one less potential tear propagation point, i.e., one less gullet in the serrate portion. The wrapping operation is then completed in this usual manner, i.e., by making four overlapped end folds at each end of the loaf, applying end labels if desired, and sealing together the end folds and end label.

Bread packages made with the wrapping sheets of this invention are much stronger than those made from the same materials, but with the old sawtooth cut over the entire width. Not only is there much less opportunity for tears in the cut edges during the sheeting and wrapping operations but also, because of the absence of serrate portions except for the relatively short band at the middle of the loaf, virtual freedom from tears in the end portions of the wrapper when it is opened by the ultimate consumer.

As applied to thermoplastic film webs not having an underlying waxed paper band the invention is essentially the same as above described with the exception of omitting the sawtooth portion of the knife shown in FIG- URE 1. In this case the cutting edge 16 of the respective straight blade portions merge at about the center line of the overall assembly. The blade bevel and taper angle in this modified construction are the same as those previously described. It will be appreciated that the cutting action of the modified knife also proceeds simultaneously from each side edge of the web on an essentially straight line. Cutting will progressively continue from each side of the web towards the center until the web is fully severed at the juncture of the two straight blade portions. This particular cutting sequence provides sheets having virtually straight, non-jagged cut edges essentially at right angles to the side edges of the web.

What is claimed is: 1. Improved sheeting knife assembly for cutting film comprising:

(a) a knife blade holder having secured thereto 1) a centrally located beveled sawtooth blade portion having teeth whose apices are in a single plane,

(2) a beveled straight blade portion extending outwardly from each side of the sawtooth portion, the cutting edge of each straight portion being immediately adjacent the cutting edge at the respective ends of the sawtooth blade and tapering downwardly toward the outer extremities of the assembly at an angle of at least 2, whereby at least a part of each straight cutting edge is below the plane of the apices of the teeth in the sawtooth portion;

(b) means in said blade holder for heating at least said straight blade portions and (c) said knife blade holder being pivotally mounted so as to rotate said knife assembly in a curvilinear path thus causing a serrated cut in the film contacted by the sawtooth blade portion and a straight line cut in the film contacted by the straight blade portion. 2. Knife assembly of claim 1 wherein the bevel angle is from about 5 to about 15.

3. Knife assembly as defined in claim 1 wherein the said sawtooth portion terminates at each of its respective ends at the base or gullet of an individual tooth.

4. Knife assembly as defined in claim 1 wherein the said sawtooth portion terminates at each of its respective ends at the apex of an individual tooth.

References Cited by the Examiner UNITED STATES PATENTS 122,260 12/71 Lake 8349 676,781 6/01 Stimpson 83698 1,085,356 1/14 Raffel 83370 1,716,991 6/29 Turner 30355 1,810,987 6/31 Schmitt 83171 1,929,838 10/33 Crane 30355 1,972,133 9/34 Darrow 83171 2,019,749 11/35 Underwood 83918 2,233,000 2/41 Chesley 8349 2,401,310 6/46 Mayhew 83-695 2,423,601 7/47 MacArthur 83689 2,517,362 8/ Thompson 83*694 2,706,238 4/55 Blaser 83170 2,727,128 12/55 Jaye 83170 2,781,843 2/57 Cornstock 83--192 3,062,432 11/62 Jacke 22987 3,066,848 12/ 62 Billeb 22987 FOREIGN PATENTS 162,131 1/ 49 Austria.

WILLIAM W. DYER, JR., Primary Examiner.

HUNTER C. BOURNE, JR., ANDREW R. JUHASZ,

Examiners. 

1. IMPROVED SHEETING KNIFE ASSEMBLY FOR CUTTING FILM COMPRISING: (A) A KNIFE BLADE HOLDER HAVING SECURED THERETO (1) A CENTRALLY LOCATED BEVELED SAWTOOTH BLADE PORTION HAVING TEETH WHOSE APICES ARE IN A SINGLE PLANE, (2) A BEVELED STRAIGHT BLADE PORTION EXTENDING OUTWARDLY FROM EACH SIDE OF THE SAWTOOTH PORTION, THE CUTTING EDGE OF EACH STRAIGHT PORTION BEING IMMEDIATELY ADJACENT THE CUTTING EGDE AT THE RESPECTIVE ENDS OF THE SAWTOOTH BLADE AND TAPERING DOWNWARDLY TOWARD THE OUTER EXTREMITIES OF THE ASSEMBLY AT AN ANGLE OF AT LEAST 2*, WHEREBY AT LEAST A PART OF EACH STRAIGHT CUTTING EDGE IS BELOW THE PLANE OF THE APICES OF THE TEETH IN THE SAWTOOTH PORTION; (B) MEANS IN SAID BLADE HOLDER FOR HEATING AT LEAST SAID STRAIGHT BLADE PORTIONS AND (C) SAID KNIFE BLADE HOLDER BEING PIVOTALLY MOUNTED SO AS TO ROTATE SAID KNIFE ASSEMBLY IN A CURVLINEAR PATH THUS CAUSING A SERRATED CUT IN THE FILM CONTACTED BY THE SAWTOOTH BLADE PORTION AND A STRAIGHT LINE CUT IN THE FILM CONTACTED BY THE STRAIGHT BLADE PORTION. 